1. Field of the Invention
The invention relates to power control for electrical circuits, and more specifically to power control for electrical circuit through reduced pin count.
2. Description of the Related Art
A power supply voltage delivered to a circuit generally determines the standard digital threshold level of the circuit (also known as the voltage standard of the circuit), and the digital threshold level of input signals should be consistent with the digital threshold level of the circuit. When an integrated circuit (IC) is coupled to a system, it has several inputs, which may include data inputs (digital inputs) from the system, a power supply, and a power control signal from the system that enables or disables the IC. Usually, the voltage standards for the IC and for the system can be different from each other. For example, the voltage standard of the system may be 1.5V, or 1.8V, while the power supply voltage to the IC may be 3.3V or 5.0V. Consequently, the IC may not be able to receive digital inputs from the system directly because of the voltage difference. It may require a conversion to adjust the voltage of the digital inputs to meet the voltage standards of the IC.
Additionally, the IC may also requires a power input signal from the system to power the digital inputs, because the power supply voltage that powers the digital inputs should be consistent with the voltage standard of the digital inputs. Therefore, the IC should have a power input pin that receives the power input signal from the system to power the digital inputs. As previously stated, the IC may also receive a power control signal from the system that instructs the IC when to power on or power down. Traditionally, an additional pin is employed by the IC to receive the power control signal. However, given the facts that the power input signal and power control signal both are generally from the same system and that it is not necessary for the IC to be powered when the system is powered off, it is desirable to have a single pin for power input and power control. As a result, the reduced pin count will advantageously reduce the power consumption and the cost. Thus, it is to such an apparatus and method that enables a single pin to support both the power input function and the power control function the present invention is primarily directed.